178 research outputs found
Emerging unitary evolutions in dissipatively coupled systems
Having a broad range of methods available for implementing unitary operations is crucial for quantum information tasks. We study a dissipative process commonly used to describe dissipatively coupled systems and show that the process can lead to pure unitary dynamics on one part of a bipartite system, provided that the process is strong enough. As a consequence of these findings, we discuss within the framework of quantum control theory how the dissipative process can enable universal control of the considered part, thereby turning parts of the system into a system capable of universal quantum information tasks. We characterize the time scales necessary to implement gates with high fidelity through the dissipative evolution. The considered dissipative evolution is of particular importance since it can be engineered in the laboratory in the realm of superconducting circuits. Based on a reservoir that is formed by a lossy microwave mode we present a detailed study of how our theoretical findings can be realized in an experimental setting
Nonreciprocal Photon Transmission and Amplification via Reservoir Engineering
We discuss a general method for constructing nonreciprocal, cavity-based
photonic devices, based on matching a given coherent interaction with its
corresponding dissipative counterpart; our method generalizes the basic
structure used in the theory of cascaded quantum systems, and can render an
extremely wide class of interactions directional. In contrast to standard
interference-based schemes, our approach allows directional behavior over a
wide bandwidth. We show how it can be used to devise isolators and directional,
quantum-limited amplifiers. We discuss in detail how this general method allows
the construction of a directional, noise-free phase-sensitive amplifier that is
not limited by any fundamental gain-bandwidth constraint. Our approach is
particularly well-suited to implementations using superconducting microwave
circuits and optomechanical systems.Comment: 15 pages, 6 figure
Parametric Couplings in Engineered Quantum Systems
Parametric couplings in engineered quantum systems are a powerful tool to
control, manipulate and enhance interactions in a variety of platforms. It
allows us to bring systems of different energy scales into communication with
each other. This short chapter introduces the basic principles and discusses a
few examples of how one can engineer parametric amplifiers with improved
characteristics over conventional setups. Clearly, the selected examples are
author-biased, and other interesting proposals and implementations can be found
in the literature. The focus of this chapter is on parametric effects between
linearly coupled harmonic oscillators, however, parametric modulation is also
applicable with nonlinear couplings and anharmonic systems.Comment: Submitted to SciPost Lecture Notes. To appear in 'Quantum Information
Machines; Lecture Notes of the Les Houches Summer School 2019', eds. M.
Devoret, B. Huard, and I. Po
Minimal Models for Nonreciprocal Amplification Using Biharmonic Drives
We present a generic system of three bosonic modes coupled parametrically with a time-varying coupling modulated by a combination of two pump harmonics, and we show how this system provides the minimal platform for realizing nonreciprocal couplings that can lead to gainless photon circulation, and phase-preserving or phase-sensitive directional amplification. Explicit frequency-dependent calculations within this minimal paradigm highlight the separation of amplification and directionality bandwidths, a feature generic to such schemes. We also study the influence of counterrotating interactions that can adversely affect directionality and the associated bandwidth; we find that these effects can be mitigated by suitably designing the properties of the auxiliary mode that plays the role of an engineered reservoir to the amplification mode space.University of Massachusetts at Lowel
Exceptional-point-based optical amplifiers
The gain-bandwidth product is a fundamental figure of merit that restricts the operation of optical amplifiers. Here, we introduce a design paradigm based on exceptional points, which relaxes this limitation and allows for the building of a new generation of optical amplifiers that exhibits a better gain-bandwidth scaling. Additionally, our results can be extended to other physical systems such as acoustics and microwaves
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